Once in Nestor and once in Proteus, Stephen thinks of the Ulster Protestants who harassed Catholic peasants in the 1780s and 90s. In the latter chapter, Kevin Egan is wearing what Stephen fancies to be "his peep of day boy's hat"—odd, since Egan was not an activist of that stripe. The Peep o' Day Boys were agrarian Protestants who staged raids on Catholic cottages in the early-morning hours. Eventually they were subsumed into the orange lodges. Stephen earlier has thought about a massacre that occurred at one of these lodges in 1795: "The lodge of Diamond in Armagh the splendid behung with corpses of papishes."
The Peep of Day Boys initiated a campaign of ethnic cleansing, seeking to force Catholics out of County Armagh. Notices reproducing Oliver Cromwell's notorious phrase "To Hell or Connaught" were posted on the doors of homes with a date, and if the cottage was not evacuated by that date it would be burned down. Catholics organized a resistance organization called the Defenders, but many thousands of Catholics left the county in 1795 and 1796. When a group of mostly unarmed Defenders gathered at "the lodge of Diamond" on September 21, they were cut down by heavily armed Protestants.
The organized resistance has allowed Protestants to remember the killings as a glorious victory over a threatening mob: in Orange Order lore they are memorialized as the Battle of the Diamond. In the Catholic cultural memory that Stephen is drawing on, the killings in Armagh were a massacre, and they hold much the same resonance that the 1972 Bloody Sunday massacre in Derry would later acquire.
Thornton notes that "Armagh the Splendid" is "a set phrase that goes back at least as far as Mangan's translation of 'Prince Alfrid's Itinerary through Ireland.'"